The Heart and Lungs at Work Chapter 6

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The Heart and Lungs at WorkChapter 6
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The Primary Roles of the Cardiovascular System

• 1. to transport oxygen from the lungs to the
  tissues
• 2. to transport carbon dioxide from the tissues
  to the lungs
• 3. to transport nutrients from the digestive
  system to other areas in the body
• 4. to transport waste products from sites of
  production to sites of excretion.

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The Heart

• Structure
• comprised of cardiac muscle that serves to pump
  blood through the human body.
• consists of four chambers
• - two ventricles (left and right) ? pump
  blood through the body,
• - two atria (left and right) ? receive blood
  from peripheral organs and pump blood into the
  ventricles
• Left ventricle ? pumps blood through the entire
  body (are larger and with stronger muscle walls
  than the right ventricles)
• Right ventricle ? pumps blood a short distance to
  the lungs

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The Heart

• Pathway of blood flow
• The right atrium receives deoxygenated blood from
  the superior and inferior vena cava
• The blood moves from the right atrium to the
  right ventricle and pumps it to the lungs
• The left atrium receives the oxygenated blood
  from the lungs and pumps it to the left ventricle
• The blood is now oxygen-rich and is transported
  to the entire body via the aorta

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The Heart
Pathway of blood flow
RIGHT ATRIUM
Tricuspid valve
RIGHT VENTRICLE
Veins
Pulmonary semilunar valve
Pulmonary arteries
Capillaries
Lungs
Pulmonary veins
Arteries
LEFT ATRIUM
Bicuspid valve
LEFT VENTRICLE
Aortic semilunar valve
Aorta
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The Heart

• Function
• The heart contracts in a constant rhythm that may
  speed up or slow down depending on the need for
  blood (and oxygen) in the body.
• The beating of the heart is governed by an
  automatic electrical impulse generated by the
  sinus node
• The sinus node is a small bundle of nerve fibers
  that are found in the wall of the right atrium
• The sinus node generates an electrical charge
  called an action potential. The action potential
  causes the muscle walls of the heart to contract.
  This action potential travels through the two
  atria and the two ventricles via the a-v node and
  the Purkinje fibres.
• The atria contract before the ventricles
  contract, which allows for the blood to be
  quickly pumped into the ventricles from the atria

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The Heart

• Blood Pressure
• This is an important measure of cardiac function.
  
• There are two components to the measure of blood
  pressure
• Systole - It is the pressure in the ventricles
  when they are contracting and pushing blood out
  into the body.
• Diastole - It is used to describe the pressure in
  the heart when the ventricles are relaxed and the
  atria are being filled with blood. Indicator of
  peripheral blood pressure (the blood pressure in
  the body outside the heart).
• FYI The normal range of pressure in the atria
  during diastole is about 80 mmHg, and during
  systole is about 120 mmHg.

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The Finely Tuned Cardiac Cycle

• (a) As the heart relaxes in diastole, both atria
  simultaneously fill with blood.

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Measuring Blood Pressure

• Blood flow is cut off at the brachial artery and
  then air is gradually released to reinitiate the
  flow

Systolic - When the pressure lessens to a point
where blood flow continues and you hear the first
sound (Systolic) Diastolic - Once the sound
desists completely and blood flow continues to
normal
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The Heart

• Stroke Volume
• The amount of blood pumped out of the left
  ventricle each time the heart beats.
• Measured in milliliters.
• A typical stroke volume for a normal heart is
  about 70 milliliters of blood per beat.
• Cardiac Output
• The amount of blood that is pumped into the aorta
  each minute by the heart.
• Cardiac output (ml/bpm) stroke volume (ml) x
  heart rate (bpm)

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Measuring Heart Rate

• Taking heart rate with fingers on wrist and neck

(a) Feeling the carotid pulse
(b) Feeling the radial pulse
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The Heart

• Heart Rate
• The number of times the heart beats in one
  minute, measured in beats per minute (bpm).
• The contraction of the walls of the heart is
  commonly known as a heart beat.
• The resting heart rate of an adult can range from
  40 bpm in a highly trained athlete to 70 bpm in a
  normal person.
• During intense exercise, the heart rate may
  increase to up to 200 bpm

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Circuitry of the Heart and Cardiovascular
System

• Illustration of the entire cardiovascular
  system heart, lungs, peripheral circulation

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The Heart

• The Peripheral Circulatory System
• The peripheral circulatory system is comprised of
  the vessels that carry blood away from the heart
  to the muscles and organs (lungs, brain, stomach,
  intestines), and the vessels that return the
  blood to the heart.
• All of the vessels of the body are made up of
  smooth muscle cells that allow them to contract
  or relax.
• The contractile properties of smooth muscle
  enable the vessels of the peripheral circulatory
  system to regulate blood flow and alter the
  pattern of circulation throughout the body.

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The Heart

• The Peripheral Circulatory System
• Vessels that carry blood away from the heart are
  called arteries.
• Arteries branch into smaller and smaller vessels
  called arterioles.
• The arterioles branch into even smaller vessels
  called capillaries.

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The Heart

• The Peripheral Circulatory System, Arteries
  contd
• Capillaries
• allow for the exchange of oxygen and nutrients
  from the blood to muscles and organs
• allow blood to pick up the waste products and
  carbon dioxide from metabolism

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The Heart

• The Peripheral Circulatory System, Veins
• As the blood begins to return to the heart, the
  capillaries connect to form larger and larger
  vessels called venules.
• The venules then merge into larger vessels that
  return blood to the heart called veins.

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The Heart

• The Peripheral Circulatory System, Veins
  continued
• In comparison to arteries, veins have valves that
  open as blood returns to the heart, and valves
  that close as blood flows away from the heart.
• Blood can be pushed through veins by smooth
  muscle that surrounds the veins, contraction of
  large muscles near the veins, or to a minor
  extent by the pumping action of the heart.

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The Skeletal Muscle Pump

• blood flow towards the heart opens the valves
• blood flow away from the heart closes the valves.

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The Heart

• Red Blood Cells
• Also called erythrocytes
• The primary function is to transport oxygen from
  the lungs to the tissues and remove carbon
  dioxide from the body. They are able to do this
  because of a substance called hemoglobin.
• Other components of blood include white blood
  cells and the clear fluid plasma. The percentage
  of the blood made up of red blood cells is called
  hematocrit (about 45).

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The Red Blood Cell

• Single red blood cell or erythrocyte

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The Heart

• Hemoglobin
• A molecule made up of proteins and iron
• Each molecule can bond to and transport four
  oxygen molecules.
• The amount of oxygen that is carried by the blood
  is dependent upon the partial pressure of oxygen
  (PO2).

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The Heart

• Hemoglobin
• New red blood cells or reticulocytes are produced
  in the bone marrow
• Erythropoietin (EPO), a circulating hormone, is
  the principal factor that stimulates red blood
  cell formation
• EPO is secreted in response to low oxygen levels
  (when one goes to altitude) and also in response
  to exercise, thus increasing the percentage of
  new red blood cells in the body
• New red blood cells contain more hemoglobin than
  older red blood cells and thus can carry greater
  amounts of oxygen

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EPO Production

• High altitude (low oxygen level) has an effect on
  EPO production which in turn generates a high
  production of red blood cells.

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Transport of Carbon Dioxide

• CO2 is produced in the body as a by-product of
  metabolism
• CO2 diffuses from the cells to the blood where it
  is transported to the lungs via one of three
  mechanisms
• 1. A small percentage of the produced CO2 is
  dissolved in the blood plasma
• 2. CO2 bonds to the hemoglobin molecule
• 3. The primary mechanism whereby CO2 is
  transported through the body is via combining
  with water to form bicarbonate molecules that are
  then transported through the body. This happens
  according to the following reversible reaction

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Oxygen Uptake

• is the amount of oxygen that is consumed by the
  body due to aerobic metabolism
• It is measured as the volume of oxygen that is
  consumed (VO2) in a given amount of time, usually
  a minute
• Oxygen uptake increases in relation to the amount
  of energy that is required to perform an activity
• (VO2max) a measure used to evaluate the maximal
  volume of oxygen that can be supplied to and
  consumed by the body

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Testing for Maximal Oxygen Uptake

• Testing maximal aerobic power (VO2max)

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Oxygen Uptake

• Changes in hematocrit (concentration of red blood
  cells in the blood) can also alter the oxygen
  uptake by increasing or decreasing the amount of
  oxygen that is supplied to working tissues.
• The ability of the tissues to extract oxygen
  (a-vO2 difference) directly affects the oxygen
  uptake.
• Increases in a-vO2 difference may arise due to an
  increased number of mitochondria in the muscles,
  or increased enzyme efficiency in working tissues

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Oxygen Uptake

• Increased capillarization (number of capillaries
  in tissue) can affect the ability of the
  circulatory system to place red blood cells close
  to the tissues that are using the oxygen.
• As a result, this increases the ability of those
  tissues to extract the required oxygen due to a
  shorter diffusion distance.

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Cardiovascular Anatomy Summary

• The primary concerns of the cardiovascular system
  are
• 1. the ability of the lungs to oxygenate the
  blood
• 2. the ability of the body to extract that
  oxygen.
• Training can increase the maximal oxygen
  consumption of the human body. How this is
  accomplished will be presented in the next
  section.